This invention relates to mechanical power transmission systems and more particularly, it concerns an improved drive line or train by which power developed by an engine may be transmitted through a wide range of continuously variable speed ranges.
In light of recent interest in fuel and energy conservation, the automotive industry has and continues to place increasing emphasis on reducing the weight and aerodynmic drag of automotive vehicles as well as on smaller and more efficient engines. Also, it is generally recognized that the operating efficiency of a given engine can be increased and correspondingly, the fuel consumption reduced, by increasing the range of speed ratios available in the drive line between the engine and the driving axle of a vehicle. For example, automotive drive lines have traditionally included multispeed transmissions to provide a range of speed ratio reductions on the order of 2 or 2.5:1 to 1:1 and a final drive gear reduction at the driving axle approximating 4:1 to provide a total speed reduction range in the drive line on the order of 8 or 10:1 to 4:1. The trend recently has been to increase this range particularly at the high speed end to provide an overdrive at the transmission output shaft for the reason that at cruising or highway speeds, where the demand for power is minimum, greater efficiency can be achieved with slower engine operating speeds than are possible with traditional speed ratio reductions. Yet, the large speed ratio reduction is required at the low speed end of the range in order to develop adequate torque for low speed operation.
It is apparent, therefore, that increasing the range of speed ratios available in a given transmission can be significant in reducing the fuel consumption of an automotive vehicle. On the other hand, increasing the speed ratios available in a gear-type transmission requires the addition of gears, shafting and control components which, in turn, add to the size and weight of the transmission. The problems associated with increased size and weight are particularly accute in front-wheel drives where the engine and transmission must be accommodated in a relatively small space.
The potential for increasing the range of speed ratios in an automotive drive line by using a continuously variable transmission unit (CVT) either along or in combination with gearing has been recognized by the automotive industry. Moreover, the state-of-the-art relating to CVT units has been advanced to a refined stage particularly in the development of a type of transmission represented by the disclosures of U.S. Pat. Nos. 4,112,779 and 4,112,780, both issued Sept. 12, 1978 and in U.S. Pat. No. 4,152,946 issued on May 8, 1979. In the type of transmission exemplified by these patents, three frame supported working bodies operate to transmit a mechanical power input to a rotatable output at continuously variable output/input speed ratios within the design range of the transmission. For purposes of definition in this background discussion as well as in the ensuing detailed description of the present invention and in the appended claims, the three working bodies may be termed respectively, and "alpha body" which is supported by the transmission frame to be concentric with a first axis, a "beta body" which is concentric with a second axis inclined with respect to and intersecting the first axis at a point of axes intersection, and an "omega body" carried by or forming part of the frame to be concentric also with the first axis. Although any one of these three bodies may be rotatable on the respective axes with which they are concentric, one of the three is held against rotation to provide a reaction torque whereas the other two bodies are rotatable and coupled either directly or by gearing to the respective input and output shafting of the transmission.
In the operation of such transmissions where an input drives the alpha body at a speed (.alpha.) to carry the beta body in nutation; the omega body is held against rotation; the beta body is linked with an output shaft rotatable at the speed (.theta.) on a first axis by gearing having a ratio factor (k); and the radius ratio of the traction surfaces on the beta and omega bodies is a variable factor (.rho.); the output/input speed ratio of the unit is determined by an equation: EQU .theta./.alpha.=1-k.rho..
The performance characteristics of such transmissions are described in an article entitled: "Performance of a Nutating Traction Drive" by P. Elu and Y. Kemper, paper no. 80-C2/DET-63, the American Society of Mechanical Engineers. In this Article, it is noted that extremely high overall efficiencies are possible by appropriate selection of the gear ratio factor (k) though with a corresponding reduction in the transmission speed ratio range (e.g., 2.8/1.9 or 1.5 vs.0.43/0 or .infin.). While a transmission which can achieve a zero output for any given input speed would, in theory, be an ideal solution to an automotive drive line because it might be combined with external gearing to provide an infinite range of speed ratios, a more practical solution lies in expanding the finite ratio ranges of such a CVT where high overall power transmitting efficiencies can be attained.
The development of drive lines using CVT units of the type described has been developed further to include inertial drive lines in which the wide range of continuously variable speed ratios may be used to transmit power directly from an engine or from a flywheel coupled with the transmission input. A clutch between the flywheel and the crank shaft of an internal combustion engine, for example, enables the flywheel to be used both as an energy storing device and as a crank shaft flywheel for the engine. The clutch is coupled at all times for rotation with the engine crank shaft when the engine is operated but allows the engine to be shut off when a kinetic energy stored in the flywheel is adequate either for restarting the engine or for propelling the vehicle. Such a drive line is disclosed in U.S. National Application Ser. No. 06/023,398, filed Mar. 23, 1979, by Yves Jean Kemper now U.S. Pat. No. 4,393,964. Corresponding National Applications have been filed in all countries designated in this International Application.